1. Field of the Invention
Embodiments of invention relate to hearing devices. More specifically embodiments of the invention relate to sealing retainers for improving the durability and comfort of continuous or extended wear hearing aids.
Since many hearing aid devices are adapted to be fit into the ear canal, a brief description of the anatomy of the ear canal will now be presented for purposes of illustration. While, the shape and structure, or morphology, of the ear canal can vary from person to person, certain characteristics are common to all individuals. Referring now to FIGS. 1-2, the external acoustic meatus (ear canal) is generally narrow and contoured as shown in the coronal view in FIG. 1. The ear canal 10 is approximately 25 mm in length from the canal aperture 17 to the center of the tympanic membrane 18 (eardrum). The lateral part (away from the tympanic membrane) of the ear canal, a cartilaginous region 11, is relatively soft due to the underlying cartilaginous tissue. The cartilaginous region 11 of the ear canal 10 deforms and moves in response to the mandibular (jaw) motions, which occur during talking, yawning, eating, etc. The medial (towards the tympanic membrane) part, a bony region 13 proximal to the tympanic membrane, is rigid due to the underlying bony tissue. The skin 14 in the bony region 13 is thin (relative to the skin 16 in the cartilaginous region) and is more sensitive to touch or pressure. There is a characteristic bend 15 that roughly occurs at the bony-cartilaginous junction 19 (referred to herein as the bony junction), which separates the cartilaginous 11 and the bony 13 regions. The magnitude of this bend varies among individuals.
A cross-sectional view of the typical ear canal 10 (FIG. 2) reveals generally an oval shape and pointed inferiorly (lower side). The long diameter (DL) is along the vertical axis and the short diameter (DS) is along the horizontal axis. These dimensions vary among individuals.
Hair 5 and debris 4 in the ear canal are primarily present in the cartilaginous region 11. Physiologic debris includes cerumen (earwax), sweat, decayed hair, and oils produced by the various glands underneath the skin in the cartilaginous region. Non-physiologic debris consists primarily of environmental particles that enter the ear canal. Canal debris is naturally extruded to the outside of the ear by the process of lateral epithelial cell migration (see e.g., Ballachanda, The Human Ear Canal, Singular Publishing, 1995, pp. 195). There is no cerumen production or hair in the bony part of the ear canal.
The ear canal 10 terminates medially with the tympanic membrane 18. Laterally and external to the ear canal is the concha cavity 2 and the auricle 3, both also cartilaginous. The junction between the concha cavity 2 and the cartilaginous part 11 of the ear canal at the aperture 17 is also defined by a characteristic bend 12 known as the first bend of the ear canal.
First generation hearing devices were primarily of the Behind-The-Ear (BTE) type. However, they have been largely replaced by In-The-Canal (ITC) hearing devices are of which there are three types. In-The-Ear (ITE) devices rest primarily in the concha of the ear and have the disadvantages of being fairly conspicuous to a bystander and relatively bulky to wear. Smaller In-The-Canal (ITC) devices fit partially in the concha and partially in the ear canal and are less visible but still leave a substantial portion of the hearing device exposed. Recently, Completely-In-The-Canal (CIC) hearing devices have come into greater use. These devices fit deep within the ear canal and can be essentially hidden from view from the outside.
In addition to the obvious cosmetic advantages, CIC hearing devices provide, they also have several performance advantages that larger, externally mounted devices do not offer. Placing the hearing device deep within the ear canal and proximate to the tympanic membrane (ear drum) improves the frequency response of the device, reduces the occurrence of the occlusion effect and improves overall sound fidelity.
However, despite their advantages, many CIC hearing devices continue to have performance issues including retention in the ear canal and acoustic feedback. Seals incorporated onto CIC devices have been used to prevent oscillatory feedback which occurs when there is acoustic leakage from the output of the hearing aid receiver through a leakage path which reaches the hearing aid microphone causing sustained oscillation. This oscillatory feedback is manifested by “whistling” or “squealing” which is both bothersome and interferes with communication. Oscillatory feedback is typically alleviated by tightly occluding (sealing) the ear canal between the microphone and the receiver. However, complete sealing can prove difficult, for example, jaw motion of the user may cause deformation of the seal and thus acoustical leakage. During jaw movement the fleshy part moves relative to the bony part so that the hearing aid and/or seal are pressed to one side of the ear canal and a gap may be formed at the other side giving rise to an acoustical leakage path causing feedback. The seal(s) can buckle due to non uniform distribution of forces on the seal and/or when the ear canal deforms resulting in an acoustical leak.
Also, the seal or hearing aid housing may not be sufficiently biocompatible or exert too much force on the ear canal epithelium resulting in one or more of irritation, inflammation, ulceration and/or infection of the epithelium and ear canal as well as thinning of the epithelium. Further, long term effects of wearing aids hearing aid are known to include chronic inflammation and atrophy of the canal epithelium and a gradual remodeling of the bony canal. Besides being uncomfortable, such conditions can require the hearing device to be removed and may actually inhibit or prevent the patient from wearing the hearing aid for extended periods of time until the canal heals. Accordingly, there is a need for a biocompatible seal for a hearing aid to comfortably retain the device in the ear canal on a continuous wear basis while reducing acoustic feedback and the risk of infection and skin ulceration.